A Statistical Study of the Magnetic Imprints of X-class Solar Flares

Abstract

Magnetic imprints, the rapid and irreversible evolution of photospheric magnetic fields as a feedback from flares in the corona, have been confirmed by many previous studies. These studies showed that the horizontal field will permanently increase at the polarity inversion line (PIL) after eruptions, indicating that a more horizontal geometry of photospheric magnetic field is produced. In this study, we analyze 20 X-class flares since the launch of the Solar Dynamics Observatory (SDO) in 15 active regions (ARs) with heliographic angle no greater than 45 • . We observe clear magnetic imprints in 16 flares, whereas 4 flares are exceptional. The imprint regions of the horizontal field are located not only at the PIL but also at sunspot penumbra with strong vertical fields. Making use of the observed mass and speed of the corresponding coronal mass ejections (CMEs) , we find that the CMEs with larger momentums are associated with stronger magnetic imprints. Furthermore, a linear relationship, with a Kendall's Tau-b coefficient 0.54, between the CME momentum and the change of Lorentz force is revealed. Based on that, we quantify the back reaction time to be ∼70 s, with a 90% confidence interval from about 50 s to 90 s.

Magnetic imprints of eruptive and non-eruptive Solar flares as observed by Solar Dynamics Observatory

“…It indicates that large change of Lorentz force leads to stronger upward impulse which drives stronger CMEs. This result is in agreement with the quite recent study of Lu et al (2019). We attributed this weak correlation is mostly due to the poor CME mass estimates in CDAW CME catalog (Vourlidas et al 2002).…”

“…In these plots, three vertical dashed lines refer to flare start (black), peak (red) and end times (black) respectively. The horizontal mag- not shown) and this enhancement of B h is permanent which is in agreement with the past studies (Wang et al 2012b;Petrie 2012;Sun et al 2017;Lu et al 2019). It is worth to point here that about 24 % (5 events) of flare events in our sample are short-time duration events of ≤ 12 m. The average B h enhancement from their preflare values for short duration events ranges from 32% to 52%.…”

“…With the launch of Solar Dynamics observatory, the continuous, high spatial and temporal resolution full disk vector magnetograms are being obtained from the Helioseismic and Magnetic Imager (HMI; Schou et al 2012) instrument on board Solar Dynamics Observatory (SDO; Pesnell et al 2012). Using 12 minute vector magnetograms, rapid and irreversible magnetic imprints on the photospheric magnetic field i.e., leading to more horizontal magnetic field structure, were observed during several major eruptions (Petrie 2012(Petrie , 2016Lu et al 2019). Wang et al (2012b) observed magnetic imprints on the photospheric magnetic field during 18 different GOES class flares (includes C-class events) and found that the vertical Lorentz force changes during flares were generally directed downward near PILs and the absolute value of these forces are well correlated with the flare strength.…”

Continuum Enhancements, Line Profiles, and Magnetic Field Evolution during Consecutive Flares

“…In this scenario, tether-cutting reconnection could be considered a plausible mechanism for the formation of the unstable flux rope (Moore et al 2001;Yurchyshyn et al 2006;Xue et al 2017;Chen et al 2016). Such a mechanism is often invoked to explain the back reaction on the solar surface that we have noticed in our observations as well (e.g., Wang & Liu 2010;Lu et al 2019). On the other hand, slipping reconnection seems to be at work during these events, as witnessed by the appearance of the bright elongated patch observed to the east of the δ-spot region a few minutes after the onset of the X1.6 flare.…”

Solar Flare Prediction Using Magnetic Field Diagnostics above the Photosphere

“…Panels Figure A6, we cannot identify the inverted V-and U-shapes before the X2.1 in the case of the second δ-spot. The reason is because the first δ-spot was actually the source of the X2.1 flare (Lu et al 2019). Figure A4).…”